A Melatonin is a natural hormone that acts on the brain to promote circadian rhythms, including sleep rhythms. Clinical trials show very tiny improvements in sleep—falling asleep four minutes sooner and 2 percent improvement in sleep time—in healthy people, and no improvement in people with other disorders such as depression.

The problem with natural melatonin is that it can't be patented, so no one has taken the expense of getting it approved by the Food and Drug Administration and producing it under FDA-controlled conditions, where the exact amount and purity is guaranteed. It's marketed instead as a “natural substance,” which means it can be sold by anyone, with virtually no controls over quality, purity, or the amount contained in a tablet. Therefore, when you get melatonin from a health-food store, there's no way to know that the pill actually contains what is claimed on the label. Studies have found an enormous range of doses in individual pills—and often not the dose that is claimed on the bottle.

Moreover, most people aren't aware of some of the side effects that can occur with melatonin. Higher doses taken for a long period of time, for example, cause testicular atrophy in men.

The bottom line: I would never take over-the-counter melatonin, because the entire supplement industry is unregulated.

An alternative, prescription ramelteon (Rozerem), activates melatonin receptors in the brain, so it works like a synthetic melatonin. Approved by the FDA last year, ramelteon has the advantage that you know exactly what you're getting. The best evidence is that, like melatonin, ramelteon decreases the time it takes to fall asleep by only a small amount. It doesn't have any effect on frequency of nighttime wakenings or total sleep time—both important for high-quality, restorative sleep.